Numerous commercially valuable plants, including common agricultural crops, are susceptible to attack by insect and nematode pests. These pests can cause substantial reductions in crop yield and quality. Traditionally, farmers have relied heavily on chemical pesticides to combat pest damage. However, the use of chemical pesticides raises its own set of problems, including the cost and inconvenience of applying the pesticides. Furthermore, chemical residues raise environmental and health concerns. For these and other reasons there is a demand for alternative insecticidal agents.
An environmentally friendly approach to controlling pests is the use of pesticidal crystal proteins derived from the soil bacterium Bacillus thuringiensis (“Bt”), commonly referred to as “Cry proteins.” The Cry proteins are globular protein molecules which accumulate as protoxins in crystalline form during late stage of the sporulation of Bacillus thuringiensis. After ingestion by the pest, the crystals are solubilized to release protoxins in the alkaline midgut environment of the larvae. Protoxins (˜130 kDa) are converted into mature toxic fragments (˜66 kDa N terminal region) by gut proteases. Many of these proteins are quite toxic to specific target insects, but harmless to plants and other non-targeted organisms. Some Cry proteins have been recombinantly expressed in crop plants to provide pest-resistant transgenic plants. Among those, Bt-transgenic cotton and corn have been widely cultivated.
A large number of Cry proteins have been isolated, characterized and classified based on amino acid sequence homology (Crickmore et al., 1998, Microbiol. Mol. Biol. Rev., 62: 807-813). This classification scheme provides a systematic mechanism for naming and categorizing newly discovered Cry proteins. The Cry1 classification is the best known and contains the highest number of cry genes which currently totals over 130.
It has generally been found that individual Cry proteins possess relatively narrow activity spectra. For example, Cry1 Ac was the first toxin to be deployed in transgenic cotton for control of H. virescens and H. zea insect pests. This toxin is known for its high level toxicity to H. virescens. However, it is slightly deficient in its ability to control H. zea and has almost no activity on Spodoptera species. Additionally, Cry1 Ab toxin has slightly less activity on H. zea than Cry1Ac but has far superior activity against S. exigua. 
Second generation transgenic crops could be more resistant to insects if they are able to express multiple and/or novel Bt genes. Accordingly, new insecticidal proteins having broad activity spectra would be highly desirable.